Vehicle body closure members, such as tailgates, are typically pivotally mounted between body side panels forming the pillars at the rear of the vehicle. The tailgate typically pivots about a hinge axis between a horizontal, open position and a vertical, closed position. Some tailgate mounting assemblies include a counterbalancing hinge assembly for assisting movement of the tailgate and counterbalancing the weight of the tailgate during opening and closing movements.
For example, U.S. Pat. No. 6,796,592 to Austin discloses a tailgate counterbalancing hinge assembly, which includes a linear torque rod, a first end assembly that pivotally retains the tailgate while permitting the torque rod to be rigidly coupled to the tailgate for movement with the tailgate about a pivot axis, and a second end assembly that pivotally retains the tailgate and permits the end of the torque rod to be rigidly retained with respect to the vehicle body. The assemblies can be mounted in the vehicle using brackets that are secured to the tailgate.
U.S. Pat. Nos. 6,793,263 and 6,769,729 to Bruford et al. disclose an automotive tailgate with a lift assist system in which the tailgate pivots about a generally horizontal pivot axis, with the tailgate including a shell defining an interior space. The tailgate is pivoted upon bearings mounted upon bearing retainers located at each end of the tailgate. A “full floating” torsion bar is disclosed which includes a first end rotationally grounded within the interior of the tailgate shell and a second end engaged with and rotationally locked with one of the bearing inserts so that the torsion bar is subjected to torsional loading as the tailgate is pivoted.
Although torque rod based tailgate counter balancing hinge designs, such as those discussed above, reduce the effort required to raise and lower a tailgate by storing energy in the twisting of the torque rod during opening/lowering, because of the residual kinetic energy stored in the tailgate, the tailgate, when free falling, can cause objectionable impact on the supports straps or on a vehicle operator. Indeed, because a tailgate can be heavy and hard to lift when being closed, or it can drop down quickly when being opened, and thus cause injury to a vehicle operator, the present invention solves these problems by de-accelerating the tailgate and having it come to a gradual stop at the open position, reducing possibility of operator injury or the gate crashing down on the check straps that mount to the vehicle box and keep the tailgate from over traveling.